The present invention relates in general to ferrite inductors for suppressing electromagnetic interference (EMI), and more particularly, to ferrite inductors for suppressing EMI emanating from rack-mounted assemblages of individual electronics units within a data center.
A cable that carries analog signals or digital signals, has a tendency to act as an antenna, radiating energy in the form of electromagnetic radiation. This tendency depends on several factors, including the frequency of the signals and the length and the geometric layout of the cable. The electromagnetic radiation emitted by a cable increases the noise level of the electromagnetic environment. That is, it may create electromagnetic interference (EMI). It is known that one or more ferrite cores may be placed on a cable to suppress the effects of EMI. To be effective, the core or cores should allow the magnetic flux produced by current in the cable to flow through the ferrite material. The EMI suppression effect of ferrite cores is reduced if air gaps exist between the cores.
Ferrite cores are generally produced by sintering suitable materials into rigid bodies, which materials are known in the art. Such materials include, for example, MnZn for lower frequencies and NiZn for middle and upper frequencies. The sintered ferrite material is dense and brittle, and can be somewhat bulky. The use of ferrite cores to suppress EMI can therefore be challenging from an electronics packaging perspective, both at the electronics unit level, as well as at the electronics rack level.
In preassembled cable assemblies, ferrite cores are typically retained on a cable at a particular location with a plastic shrink-wrap. Cables may also be retrofit with ferrite cores by mounting the cores in plastic housings that are then clipped or clamped directly to the cable. Both of these ferrite core solutions for reducing EMI require customization of many cables, such as input/output signal cables for an electronics rack. This can result in significant engineering and inventory expenses for a large amount of cable part numbers.